1. Field of the Invention
The present invention relates to an ultrasound type treatment apparatus used for the resection of a living tissue or the fracture of a stone in the body cavity of a human being.
2. Description of the Related Art
Generally, this type of treatment apparatus amplifies an ultrasonic oscillation, generated from an ultrasonic oscillation element, by a horn and transmits it to an ultrasound transmission member. The resection of the living tissue, fracture of the stone, etc., are performed with an oscillation energy of an ultrasonic wave transmitted to the distal end of the ultrasound transmission member.
In the case where the resection of the living tissue, the fracture of a stone in the body cavity, etc., are done with the use of the treatment apparatus, a liquid medium is flowed through a space defined between an ultrasound transmission member and a sheath covering the ultrasound transmission member to give an ultrasonic oscillation to an affected or diseased region while cleaning the region with the liquid medium. At the same time, the emulsified form of the living tissue or fractured stone for example is removed to an outside through a suction passage provided in the ultrasound transmission member. The liquid medium serves as a coolant for preventing the destruction of the ultrasound transmission member due to a fatigue involved.
In the aforementioned ultrasound type treatment apparatus, the liquid medium supplied from the distal end of the sheath to the diseased region is almost all atomized by the ultrasound oscillation of the ultrasound transmission member. This phenomenon prevents a field of view by the operator, such as a doctor. In the microsurgery under the microscope, the whole field of view is blocked by the atomized liquid medium, failing to perform a microsurgery on the diseased region.
Further, if the amount of liquid medium to be supplied is reduced to an extent to which no field of observation is blocked, the cooling of the ultrasound transmission member and ultrasound oscillation element is not adequate, failing to generate oscillation with a larger amplitude. This is liable to generate an abnormal heat generation in the ultrasonic oscillation element and a destruction of the ultrasound transmission member.
In order to eliminate such drawbacks, an attempt has been made in U.S. Pat. No. 4,516,398 to provide a leak hole near the distal end portion of the ultrasound transmission member and suck some of the liquid medium in the sheath through the leak hole.
In such an ultrasound type treatment apparatus, however, it is possible to cool the ultrasound transmission member and ultrasonic oscillation element. In this case, almost all liquid medium supplied from the distal end of the sheath gathers at the distal end of the ultrasound transmission member and atomized toward the diseased region in the foreground, failing to secure a better field of observation.
Further, since the ultrasound transmission member is usually narrowed or tapered toward its distal end and hence becomes thinner at or near its distal end. At the time of the ultrasonic oscillation, a greater axial force acts upon that area near the distal end of the ultrasound transmission member. It is, therefore, necessary to enhance the mechanical strength at or near the distal end portion of the ultrasound transmission member. If a leak hole which may cause a mechanical defect is provided at or near its distal end, the mechanical strength of the ultrasound transmission member is lowered, sometimes causing the failure of the ultrasound transmission member at or around the leak hole.
Published Unexamined Japanese Utility Model Application 61-43454 has proposed providing a leak hole at a minimum amplitude site of an ultrasound transmission member in view of the withstanding characteristic of the ultrasound transmission member.
In this case, some of a liquid medium flowed in the sheath from a base end is sucked by the leak hole provided partway of the ultrasound transmission member, leaving only a smaller amount of liquid medium available at an area between the leak hole and the distal end of the ultrasound transmission member. The ultrasound transmission member has to be cooled with such a smaller amount of liquid. Since cooling is inadequate at the distal end portion of the ultrasound transmission member, high temperature is involved at the distal end portion of the ultrasound transmission member so that a heat injury occurs at the normal living tissue near a diseased region or the ultrasound transmission member is destroyed due to its metal fatigue.